2. As mentioned in the previous article, when a large-diameter steel pipe is used, the material is pulled to the outside, and the neutral axis of internal pressure is located at a different position from the bending method. In top bending (compression bending), the neutral wheel is about 1/3 away from the outer wall, and when turning (swivel bending), the neutral wheel is about 2/3 away from the outer wall. Therefore, it is beneficial to use the rotary bending method to bend thin-walled pipes.

　　
　　3. Bending accuracy is also one of the factors that affect the quality of large-diameter steel pipes. When manufacturing curved tires, in addition to requiring the specification and size to be controlled within a certain tolerance range, users are also required to select the corresponding curved tires according to the diameter of the bending tube.
　　
　　4. The bendability and surface corrosion of the large-diameter steel pipe itself may also affect the quality of the large-diameter steel pipe. In the on-site construction, the operator also needs to understand the material, processing performance and surface corrosion of the processed pipe production judgment.

　
When selecting the relationship between the diameter of the large-diameter steel pipe and the wall thickness, the curve (bending radius/pipe outer diameter) can be used as a reference for users. This figure mainly reflects the influence of relative bending radius and relative wall thickness on the quality of large-diameter steel pipes. According to the pipeline processing and acceptance specifications, 4d for medium and low pressure cold-formed steel pipes and 5d for high-pressure steel pipes. Therefore, our bending design is R=4d (special circumstances will be determined separately), so for the large diameter steel pipe machine produced by our factory, the main choice is the relative wall thickness of Sx. The upper part of the drawing is the coreless area, and the middle part of the drawing is the ordinary core. Zone, the lower part of the drawing is a special core zone. Due to the difficulty in designing and manufacturing special mandrels, the operation is inconvenient.

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